Reference is made herein to copending, commonly owned U.S. Ser. No. 512,829 entitled OFF-LINE PROGRAMMABLE ROBOT. As discussed therein, in the context of an articulated robot, maintaining an identifiable relationship between the robot and the workpiece is nigh unto impossible. This is especially true when the robot is mounted to a track to extend its work envelope. Therefore, it is desirable to implement a scheme whereby the positional relationship between the robot and the workpiece is easily identifiable each time the robot moves to a new work station.
A scheme for determining the positional relationship between the robot and the workpiece involves manually directing an end effector (pointer) to four precise points on the workpiece, or on a fixture that holds the workpiece, and collecting coordinate data in three dimensions at each of the four points on the workpiece to generate an offset vector (L), representative of the robot coordinates of a workpiece zero-point and a three-by-three matrix that accounts for the rotation between the two frames of reference (See Robotics Today, Summer 1981, ppgs, 30-35, Tarvin, Ronald L., "An Off Line Programming Approach"). A disadvantage of this approach is a high degree of operator interaction which can be extremely time consuming. Furthermore, the collection of three "good" datum at each reference point requires a high degree of accuracy in many robotic axes, simultaneously.